1. Field of the Invention
This invention relates to a device for detecting short-circuiting failure of a field effect transistor (FET) which is used to control a motor for driving a power window equipped with an e.g. “finger-jammed” (hereinafter referred to as simply “jammed”) preventing function.
2. Description of the Related Art
A proposed technique for detecting failure of the FET used for drive-control of the motor is to measure a drain current or reduction of a forward voltage due to excessive heating which is attributable to the excessive current flowing through the FET.
In the proposed technique, failure of the FET is detected on the basis of the changing rate of the drain current which is a load current flowing when a motor serving as the load is actually rotated in a state where the EET is connected to the motor.
However, the detection of the failure based on the drain current may provide the following disadvantages.
(1) Excessive load is applied to the motor so that when the large drain current flows the failure is erroneously detected.
(2) If a high threshold value for deciding the excessive drain current is set to detect the failure, when a finger is jammed in a power window, this fact can be recognized only after the drain current when the finger is tightened to apply the excessive load to the motor has been detected. This leads to an in crease in the load for detecting that the finger has been jammed.